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From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe LEROY <christophe.leroy@c-s.fr>, linuxppc-dev@ozlabs.org
Subject: Re: [PATCH 1/5] powerpc/asm: Add a patch_site macro & helpers for
 patching instructions
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Date: Thu, 09 Aug 2018 19:52:27 +1000
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Christophe LEROY <christophe.leroy@c-s.fr> writes:
> Le 08/08/2018 =C3=A0 18:30, Christophe LEROY a =C3=A9crit=C2=A0:
>> Le 23/07/2018 =C3=A0 17:07, Michael Ellerman a =C3=A9crit=C2=A0:
...
>>> diff --git a/arch/powerpc/include/asm/code-patching.h=20
>>> b/arch/powerpc/include/asm/code-patching.h
>>> index 812535f40124..b2051234ada8 100644
>>> --- a/arch/powerpc/include/asm/code-patching.h
>>> +++ b/arch/powerpc/include/asm/code-patching.h
>>> @@ -32,6 +32,8 @@ unsigned int create_cond_branch(const unsigned int=20
>>> *addr,
>>> =C2=A0 int patch_branch(unsigned int *addr, unsigned long target, int f=
lags);
>>> =C2=A0 int patch_instruction(unsigned int *addr, unsigned int instr);
>>> =C2=A0 int raw_patch_instruction(unsigned int *addr, unsigned int instr=
);
>>> +int patch_instruction_site(s32 *addr, unsigned int instr);
>>> +int patch_branch_site(s32 *site, unsigned long target, int flags);
>>=20
>> Why use s32* instead of unsigned int* as usual for pointer to code ?
>
> Forget my stupid question, I didn't see it was a relative address and=20
> not an absolute one.

No worries.=20

It is a bit non-obvious at first glance, it looks like the s32 * points
to the instruction. But it points to the s32 that holds the relative
offset from itself, of the instruction.

We could add a typedef to try and make that more obvious, but I
generally don't like typedefs that hide pointerness.

cheers